U.S. Pat. No. 3,740,754 is one of the earliest patents in which a dual-polarized antenna is described. This patent describes an oscillator consisting of two metal tubes which are connected to each other along a proper folding line and placed on a one reflecting cup, and the two groups of oscillators are respectively fed by two groups of coaxial cables. Subsequently, in order to extend the working band thereof, hundreds of different dual-polarized antennas have been developed.
U.S. Pat. No. 4,184,163 describes a broadband dual-polarized antenna. In this patent, the oscillator arm of the antenna consists of a metal ring which is in a finger ring shape or a square block shape. U.S. Pat. Nos. 5,481,272, 5,952,983, 6,028,563 and 60,724,39 describe several types of oscillators, including folded grid oscillators, tie oscillators and oscillators having additional PCB baluns.
In U.S. Pat. No. 6,747,606B2, US2005/0253769A1, US2013/0106668A1 and Chinese Patents CN201435451Y, CN102025023A, CN201845867U and CN102074781A, several types of crossed oscillators are described, and those oscillators include a radiation oscillator arm consisting of two branches to improve the lobe width.
Since crossed dipoles generate a wide lobe in the horizontal plane, in order to reduce the lobe width thereof, many more complex radiators have been invented. U.S. Pat. No. 5,940,044 describes an inclined dual-polarized antenna. Such an antenna has a horizontal half-power beam width of about 65°. This antenna includes several dipole sub-arrays, and each dipole is formed by arranging four single-dipoles in a rhombic shape, a diamond shape or regular cube shape. In this way, dipole sub-arrays are formed. Two single-dipoles in each dipole sub-array and the long sides of the reflecting plate are designed to be inclined at an angle of +45°. In this way, a +45° polarized radiation unit array is formed. The other two single-dipoles and the long sides of the reflecting plate are designed to be inclined at an angle of −45°. In this way, a −45° polarized radiation unit array is formed. In this patent, those dipoles are arranged in such a way that the phase centers of one +45° single-dipole and one −45° single-dipole, on a same side, are arranged along a first vertical line parallel to the long sides of the reflecting plate. Similarly, the phase centers of the other +45° single-dipole and one −45° single-dipole are arranged along a second vertical line. Such square dipoles have a major defect that one complex feeding network is required, for example, the four single-dipoles must be respectively fed by four coaxial cables.
EP0973231A2, U.S. Pat. No. 5,633,372B1, U.S. Pat. No. 6,529,172B2 and US2010/0309084A1 describe several radiators having a square pattern. For ease of manufacturing, the baluns of those dipoles are inclined with respective to the center line of the pattern of the square oscillator. Although it is a novel graphic structure, it is still very complex to manufacture such antennas.
U.S. Pat. No. 6,313,809B1 describes a dual-polarized radiator consisting of four single-dipoles. This radiator is appropriately placed on a reflector. When viewed from the top, the overall structure thereof is square. Each of the dipoles is fed by symmetric lines and has the following feature: the dual-polarized dipole radiator, in the electric aspect, radiates by using a polarization forming an angle of +45° or −45° with a structurally specified dipole. In this way, the ends of the symmetric lines of ½ dipoles are crisscross connected, that is, the respective ½ lines of the adjacent and vertical ½ dipoles are always electrically connected; and for the first polarization and the second polarization orthogonal to the first polarization, decoupling is realized, and it is able to electrically feed the opposite ½ dipoles, respectively.
Some other modifications of such square dipoles have been described in U.S. Patents and Chinese Patents U.S. Pat. No. 6,940,465B2, U.S. Pat. No. 7,688,271B2, CN202423543U, CN202268481U, CN101916910A, CN102097677A, CN102694237A, CN102544711A, CN201199545Y, CN102117967A and CN102013560A.
Patent WO2007/114620A1 describes a dual-polarized radiator consisting of four folded oscillators. This radiator employs a same arrangement as U.S. Pat. No. 6,313,809B1, and is properly placed on a reflecting plate. Some other medications of such folded oscillators have been described in Chinese Patents CN101707292A, CN201430215Y, CN202178382U and CN202004160U. In addition, Chinese Patents CN102377007A, CN201117803Y, CN201117803Y and CN101505007A describe formation of one square dipole pattern by capacitive coupling of several folded oscillators and one single-dipole.
When the bandwidth reaches 30%, forming one square dipole by those known radiators including four common or folded oscillators can provide a good directional diagram. However, those dipoles need a wide reflecting plate to generate a good front-to-back ratio. When a radiation deployment device thereof is placed on one reflecting plate, the height of the oscillators is approximately ¼ wavelengths of the center working frequency. Hence, the known radiators have a large size.
In order to overcome those defects, many other dual-polarized radiators having a small size have been invented. U.S. Pat. Nos. 6,933,906B2, U.S. Pat. No. 7,132,995B2 and US2012/0235873A1 and Chinese Patents CN102074779A, CN102157783A, CN101707291A, CN101572346A, CN201741796U, CN101546863A, CN101673881A, CN202150554U, CN102246352A, CN102484321A, CN202423541U, CN102544764A and CN101707287A describe many crossed dipoles having different oscillator arms. In the horizontal plane, since the lobe width of crossed dipoles is too large, it is necessary to reduce the lobe width by a large side. In this way, the size of the antenna may still be very large, for example, as described in U.S. Pat. No. 7,679,576.
Patent WO 2007/114620A1 describes a square dipole formed of a folded oscillator consisting of one connection portion and a connected oscillator arm. U.S. Patent US2009/0179814 A1 describes a dual-polarized broadband antenna, the radiation device of which includes folded oscillators, as the prior art, and FIG. 1 shows a radiator thereof.